Theses and Dissertations (Chemistry)http://hdl.handle.net/10500/2738
Fri, 09 Dec 2016 15:28:36 GMT2016-12-09T15:28:36Z2-ARYL-6,8-Dibromoquinolinones as synthons for the synthesis of Polysubstituted 4-ARYL-6-Oxopyrrolo [3,2,1-ij] Quinolineshttp://hdl.handle.net/10500/21206
2-ARYL-6,8-Dibromoquinolinones as synthons for the synthesis of Polysubstituted 4-ARYL-6-Oxopyrrolo [3,2,1-ij] Quinolines
Oyeyiola, Felix Adetunji
The known 2-aryl-6,8-dibromo-2,3-dihydroquinolin-4(1H)-ones 122 were dehydrogenated
using thallium(III) p-tolylsulfonate in dimethoxyethane under reflux to afford the 2-aryl-6,8-dibromoquinolin-4(1H)-ones 136. Palladium-catalyzed Sonogashira cross-coupling of the 2-aryl-6,8-dibromo-2,3-dihydroquinolin-4(1H)-ones with terminal alkynes in the presence of PdCl2(PPh3)2-CuI (as homogeneous catalyst source) and 10% Pd/C-PPh3-CuI (as heterogeneous catalyst source) catalyst mixture and NEt3 as a base and co-solvent in ethanol under reflux afforded the corresponding 6,8-dialkynyl-2-aryl-2,3-dihydroquinolin-4(1H)-ones 138 and 8-alkynyl-2-aryl-6-bromo-2,3-dihydroquinolin-4(1H)-ones 137, respectively. PdCl2-catalyzed
electrophilic cyclization of the 8-alkynyl-2-aryl-6-bromo-2,3-dihydroquinolin-4(1H)-ones in acetonitrile under reflux afforded the 4-aryl-8-bromo-2-phenyl-6H-pyrrolo[3,2,1-ij]quinolin-6-ones 139 or the 2-aryl-6-bromo-8-(4-hydroxybutanoyl)-2,3-dihydroquinolin-4(1H)-ones 140 from the 4-phenylethynyl-substituted or 4-alkylethynyl-substituted precursors, respectively. The 2-aryl-6,8-dibromoquinolin-4(1H)-ones 136 wturn, subjected to similar homogeneous and heterogeneous palladium catalyst sources using NEt3 as a base in DMF-water mixture under reflux and K2CO3 as a base in dioxane under reflux afforded 2,8-disubstituted 4-aryl-6-oxopyrrolo[3,2,1-ij]quinolines 143 and 2-substituted 4-aryl-8-bromo-6-oxopyrrolo[3,2,1-ij]quinolines 142, respectively. The monoalkynylated 4-aryl-8-bromo-2-phenyl-6H-pyrrolo[3,2,1-ij]quinolin-6-ones 139 and 2-substituted 4-aryl-8-bromo-6-oxopyrrolo[3,2,1-ij]quinolines 142 were subsequently transformed using palladium-catalyzed Suzuki-Miyaura cross-coupling with arylboronic acids in the presence of PdCl2(PPh3)2-PCy3 catalyst mixture and K2CO3 as a base in dioxane-water mixture to afford the corresponding novel 8-substituted 2-phenyl-6H-pyrrolo[3,2,1-ij]quinolin-6-ones 141 and 2,8-disubstituted 4-aryl-6-oxopyrrolo[3,2,1-ij]quinolines 144, respectively. All the new compounds were characterized using a combination of 1H NMR, 13C NMR, IR, mass spectroscopic techniques and X-ray crystallography.
Tue, 01 Sep 2015 00:00:00 GMThttp://hdl.handle.net/10500/212062015-09-01T00:00:00ZDispersive liquid-liquid micro-extraction of steroidal hormones and determination in wastewater using high pressure liquid chromatography: charged aerosol detectorhttp://hdl.handle.net/10500/19733
Dispersive liquid-liquid micro-extraction of steroidal hormones and determination in wastewater using high pressure liquid chromatography: charged aerosol detector
Osunmakinde, Cecilia Oluseyi
Steroid hormones belong to a group of compounds known as endocrine disruptors. They are hydrophobic compounds and are categorized as natural and synthetic estrogens. Some common household products have been implicated as estrogen mimics. Exposure effects of these compounds are felt by human and wildlife, such reproductive alterations in fish and frogs. They mainly introduced into the environment through veterinary medicines administration to animals and the discharges from wastewater treatment plants (WWTPs).
In this study, a new alternative analytical procedure that is simple, rapid and fast for the determination and quantification of five steroidal hormones: estriol (E3), beta estradiol (β-E2), alpha estradiol (α-E2), testosterone (T), progesterone (P) and bisphenol A (BPA) using the High pressure liquid chromatography coupled to a charged aerosol detector (HPLC-CAD). These compounds were studied because of their strong endocrine-disrupting effects in the environment.
Under optimum conditions, a linear graph was obtained with correlation coefficient (R2) ranging from 0.9952 - 0.9996. The proposed method was applied to the analysis of water samples from a wastewater plant and the results obtained were satisfactory. The limits of detection (LOD) for the target analytes in wastewater influent was between 0.0002 – 0.0004 μg/L and the limit of quantification (LOQ) was 0.001 μg/L respectively for each of the analytes. Enrichment factors of 148- 258, and extraction efficiency 84- 102% were obtained for the target analytes; relative standard deviations (% RSD) for m = 6 were between 2.8 and 7.6%. The concentration of the EDCs in environment sample was between 0.2 - 2.3 μg/L.
Wed, 01 Oct 2014 00:00:00 GMThttp://hdl.handle.net/10500/197332014-10-01T00:00:00ZCharacterization of silk proteins from African wild silkworm cocoons and application of fibroin matrices as biomaterialshttp://hdl.handle.net/10500/19145
Characterization of silk proteins from African wild silkworm cocoons and application of fibroin matrices as biomaterials
Mhuka, Vimbai
Challenges in treating injuries, together with an increased need for repair of damaged tissues and organs, have made regenerative medicine a major research area today. Biomaterials such as silk fibroin (SF) have proven to be excellent tissue scaffolds possessing properties essential in tissue engineering such as biocompatibility, biodegradability and exceptional mechanical properties. SF nanofibres are especially attractive due to their large surface-to-volume ratio and high porosity which is beneficial in regenerative medicine. However, to design biomaterial scaffolds, chemical and physical properties of SF have to be sufficiently known. The thesis aims to contribute to knowledge by characterizing silk fibroin from the African wild silkworm species Gonometa rufobrunnae, Gonometa postica, Argema mimosae, Epiphora bahuniae and Anaphe panda. Moreover, the feasibility of producing nanofibrous biomaterial scaffolds from these fibroins is explored.
The chemical composition of degummed fibres was investigated using Capillary electrophoresis whilst Infrared (IR) and Raman spectroscopic techniques were utilized to determine structural characteristics of the fibroin. In addition, thermal behaviour and mechanical properties of the fibroins were also investigated. Nanofibres were fabricated via electrospinning. The effects of solution concentration, voltage, polymer flow rate and tip to collector distance were studied to give optimum electrospinning conditions. IR spectroscopy was also utilized to observe the conformational structure of the degummed and electrospun fibres whilst scanning electron microscopy (SEM) provided information on the size and morphology of the fibres. The use of the nanofibres as biomaterials was evaluated using cytotoxicity tests.
Results showed that glycine, alanine and serine constituted over 70% of the amino acid composition of all the fibroins. Gonometa fibroin had more glycine than alanine whilst the opposite was true for Argema mimosae, Epiphora bahuniae and Anaphe panda fibroin. The abundance of basic amino acids in Gonometa rufobrunnae, Gonometa postica, Argema mimosae and Epiphora bahuniae fibroin makes them prime candidates for cell and tissue culture. The amino acid composition of the fibroins influenced secondary structure as the β-sheet structure. Anaphe panda, Argema mimosae and Epiphora bahuniae silks was made up of mostly alanine-alanine (Ala-Ala)n polypeptides whilst Gonometa fibroin had an interesting mixture of both glycine-alanine (Gly-Ala)n and (Ala-Ala)n units. The unique structures impacted the mechanical and thermal properties of the fibroins.
Production of Gonometa nanofibres was mainly dependent on fibroin solution concentration. A minimum of 27 % w/v was needed to produce defect free nanofibres. Diameters of the electrospun fibres produced ranged from 300 to 2500 nm. IR spectroscopy data highlighted that the β-sheet conformation of degummed fibroin was degraded during the formation of the nanofibres rendering them water soluble. It was however possible to regenerate the β-sheet structure in the nanofibres by exposing them to various solvents. Cytotoxicity tests using Sulforhodamine B (SRB) assay demonstrated that the nanofibres were not toxic to cells, a major prerequisite for use as a biomaterial.
This thesis successfully provides useful data in an area that has been minimally explored. Results suggest that SF from African silkworm species offers diversity in properties and are therefore attractive for use as biomaterials, especially in cell and tissue engineering. As far as we could determine, we are the first to extend the use of fibroin from African silk species by producing Gonometa SF nanofibres that are of potential use as biomaterial scaffolds.
Sat, 01 Nov 2014 00:00:00 GMThttp://hdl.handle.net/10500/191452014-11-01T00:00:00ZTeaching chemistry of water purification in grade 11 using locally available materials through the scientific inquiry approachhttp://hdl.handle.net/10500/19033
Teaching chemistry of water purification in grade 11 using locally available materials through the scientific inquiry approach
Makoni, Robert Davison
This dissertation surveyed the validities of teaching the chemistry of water purification in
South African schools using locally available materials (LAM) through the scientific inquiry
(SI) approach. The researcher randomly selected four secondary schools that provided a small
and purposive study sample of thirty-two Grade 11 learners and four teachers. The research
design applied a mixed-method approach, consisting of qualitative and quantitative methods
of data collection. Within this approach, the outcome of SI instruction that integrated LAM
was compared with that of conventional instruction through a quasi-experimental control
groups design. The researcher identified in the analysis of interviews and questionnaires the
most complex aspects of the chemistry of water purification for learners to understand as
redox reactions, acid-base systems, precipitations, and chlorination. However, the use of
LAM through the scientific inquiry approach made it easier for learners to understand the
concepts.
The high mean scores ( =80.88; SD=10.28) in Research-based Test 2 (RBT2), of the
experimental groups taught through SI signified that those learners immensely benefited from
an active and collaborative learning environment. The lowly scores ( =61.69; SD=4.21) of
control groups could be attributed to a linear and passive participation of learners in the
conventional classroom instruction. The marks of the two groups in post-test RBT2 were
paired and contrasted using GraphPad software. The results showed that t =6.699, df =21
with a significant value of 0.0001, which is less than 0.05 (p<0.05), hence it can be inferred
that the difference between the means of the two groups was not only statistically important
but also worth an explanation. The higher performance scores in RBT2 and the Rubric
Assessment Tool (RAT) in experimental groups represents that the intervention was
successful in the implementation of instructional design in the the study. In addition, the
learners had mastered the crucial aptitudes that included self-discipline in understanding,
cooperative learning, searching relevant text on topic, hands-on or laboratory practice and
logical thinking in problem solving by working through the SI activities that used LAM.
Wed, 01 Oct 2014 00:00:00 GMThttp://hdl.handle.net/10500/190332014-10-01T00:00:00Z